Manufacture of cellulose esters having a high propionyl or butyryl content



Patented June 26, 1945 MANUFACTURE OF CELLULOSE ESTERS HAVING A HIGH. PROPIONYL OR BUTYBYL CONTENT Carl J. Malm and Luring W. Blanchard, Jr., Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application April 20, 1942 Serial No. 439,720

.QClaims. (01.260-225) tion and a Zinc chloride catalyst are employed in the'esterification bath.

In the making of cellulose esters having a high propionyl or butyryl content, much care has been necessary to prepare high viscosity products due to I the sluggish nature of propionic and butyric anhydrides, compared with acetic anhydride, which, with the usual esterification procedures, necessitates severe reaction conditions.

One object of our invention is to provide a process for making high propionyl or highbutyryl cellulose esters of high viscosity in which the rigid temperature control formerly thought necessary can be dispensed with. Other objects of our invention will appear herein,

We have found that in the making of high propionyl or butyryl cellulose esters with an anhydride concentration in the esterification mixture of at least 60-per cent and zinc chloride as the catalyst, cellulose may 'be easily esterified with butyric or propionic anhydride at an elevated temperature without detrimentally affecting the physical properties of the final product. With sulfuric acid catalyst, which has heretofore been thought necessary for. preparing-high propionyl or high butyryl cellulose esters of good quality, careful restriction of the temperature has been necessary. By our invention, in which elevated temperatures are employed, a smooth homogeneous mass is obtained, and the higher temperature also enhances the solvent action of the liquid on the cellulose ester formed, facilitating the operation.

The cellulose which is employed as the starting material in a process according to our invention is preferably one which has been activated by pretreatment with a lower fatty acid but which contains but a comparatively small proportion of fatty acid when mixed with the esteriflcation' reagents. The pretreatment of cellulose, described and claimed in Malm Patent No. 2,342,415, is admirably suited for preparing cellulose for esterification in a process in accordance with our invention. Other pretreatment processes of a related nature and which are also eminentlysuited for activating the cellulose for esterification' by .our process are those described and claimed in Malm Patents Nos. 2,358,080 and Another method of pretreatment which may be employed to activate cellulose which is suitable for use in our process is that described and claimed in Malm Patent No. 2,150,690, particularly when the treatment leaves but a very small proportion of pretreatment liquid on the cellulose. If desired the cellulose to be esterified may be presoaked in acetic acid with or without a small proportion of sulfuric acid, and after the fiber has been activated to the desireddegree, the liquid is removed from the cellulose, such as by pressing, centrifuging, or by a washing operation that will leave the cellulose in active condition and with only a small proportion of acid thereon. It is desirable that the cellulose employed in our esterification process contain as little fatty acid as possible so that a. high anhydride concentration may be employed without an excessive ratio of liquid to cellulose in'the esterification bath. Also, the proportion of sulfuric acid on the cellulose if any is present, should be less than /2 per cent so that no appreciable effect is exerted thereby under the esteriflcat-ion conditions employed.

Another pretreatment method which may be employed is that described and claimed in Gardner Patent No. 2, 13,301, dated April 5, 1938, providing that the liquid remaining on the cellulose is not too great. Ordinarily it is desirable that the cellulose contain less than two parts of pretreating liquid per part of cellulose.

One of the features of our esterification process is that the anhydride concentration in the esterification liquid should be at least 60 per cent. In order to carry out such an esterification economicalhr, it is desirable to'restrict the ratio of liquid to cellulose therein to less than 6:1, such as 4.75:1. This is only possible by employing a cellulose starting material having after its pretreatment only a very low proportion of retained acid mixed therewith, preferably part per part of cellulose.

An esteriiication using a low liquid to cellulose ratio for preparing cellulose esters having a high propionyl or butyryl content to ether with a sulfuric acid catalyst is described and claimed in ,Blanchard application Serial No. 315,619, filed January 25, 1940. In the process of that application, the maximum temperatures to obtain high viscosity cellulose esters are fairly critical. Our invention possesses the advantages of a high anhydride concentration, as shown in that application, but in addition performs the esterification under most favorable conditions but without any derogatory action upon the product prepared thereby.

Our invention includes, as a feature, the esterification of the cellulose in which all or substantially all or the esteriilcation catalyst employed pounds of p opionic i e. 15 p s o p ois zinc chloride. The zinc chloride is ordinarily pi a and 10 o ds o z c hloride was employed in the esteriilcation mass in an amount mixed W the m and the temperature w from 15-100 per cent, based on the weight of the slowly raised from 1 W a period cellulose, using as a maximum temperature for of 5 hours, at which temperature the mass was the esteriflcation one selected from the range maintained 1' 5% hours lon r- The cell lose 100-160 F. had dissolved forming a smooth, homogeneous Our invention is adapted to th rep r of dope. A mixture of 30 pounds of water and 150 both the simple esters, such a cellulos proplpounds of acetic acid was added, followed by the mate and cellulose butyrate, and th ix d 65-310 addition of 100 cc. of hydrochloric acid in ilve ters, such as cellulose propionate butyrate as pounds of acetic i to speed p he rate f well as those containing in addition to the fatty hydrolysis. One portion of the mass was hydroacld groups of 3-4 arb atoms (propionyl lyzed for 150 hours, giving a cellulose propionate and/or butyryl) other acyl groups such as acetyl, havi perlcent propionyl and a viscosity, at. I, for in t t preparation of cellulose 10 per cent acetone concentration, of 373 cps. butyrate is d ir d, one may proceed by using ,The other portion of the mass was hydrolyzed for only part or butyric acid for 1 part tt 205 hours, and the propionyl content was 49,5 in the pretreatment a d 4 e of butyrjc m per cent, and the viscosity 405 cps. After the dride in the esterification. The anhydrid c nydrolysis had been completed in each case, the. centration at the beginning of the reaction is esters Were P pi ate in aqueous lower fatty 88.9 per cent, and at the end-of the esterification acid and were Washed and driedthere' is only 1.37 parts of liquid iorl part of We claim: cellulose tributyrate. Due to the high tempera- A method of Preparing as viscosity ture at th end of t e eacfl n the solution a lulose ester containing at least of saturated smooth and homogeneous in spite of the high 5 acid groups carbon atomswhich @0111- fundamental viscosity oi the cellulose butyrate so prises esterifyms, en a temperature reaching and prepared, maintained at 125-160 F., 1 part of cellulose with Qur process in its broadest aspects comprises less than 6 parts oi an esteriiication mixture or tak refined cellulose, such as refined cotton which at least 60% is anhydride of saturated fatty u t or wood pulp. which been pretreated 30 acid 01 3-4 carbon atoms, which mixture contains or activated to the desired degree but which 0011- 154.00% (based On the weight of the cellulm) t m no more than 2 parts of preheating liquid or zinc chloride as the esteriiication catalyst, is t 1 of cellulose and no more than per cent substantially iree of sulfuric acid and contains a oi. sulfuric oicid or other catalyst and mixing it sumclent of saturated fatty acid a with promomc and/or butmc hydride and groups of iilvcarbon atoms so as to result in a pounds oi water was added to 20 pounds or cotton acetic acid and 500 cc. of hydrochloric acid was at 10 per cent concentration of over 300 centiwith zinc chloride so that at least 60 per cent content of those groups in the product of at least the liquid present is anhydride and the zinc chioper ride is'15-100 per cent of the cellulose and react-' A method of preparmg a lush viscosity cek in: together the anhydride and the cellulose so lmose Faster m at least 30% butyrlwhich that amaxlmum temperature between 100 F. and 40 compnses estemymg temperature reaching F. is reached E and maintained at 125-160 F., 1 part or cellulose The follo in examples illustrate r new with less than 6 parts or an esteriiication mixture on: orwhicn at least 60% is butyric anhydride, which Example I mixture contains 15-l00% (based on th weight oi the cellulose) of zinc chloride as the esterinca- A mixture 01' 20 po nds of b yrl cid nd 2 tion catalyst, is substantially Iree oi suliuric acid and contains a sum'cient portion or butyryl so as 23:22:11: ttlzfnnpieaisastgrzs gf1i1ao5togethzr Ifor 1Z 1:; fesltlgoin a buigyryl content in. the product 0! urth eas percen. 1: 1 m 8:! 1131325111381. 0% igitgrs wasmgde, and the 3. A method or preparing a cellulose ester hav- 100 F ours an coo ed to inges butyryl content or approximately 50% and a a acetone viscosity 0: more than 300 centi- 14 c a 621120111123: 8:821:52; tznfigdgideggva; poises, which comprises esteniying at a temperzinc chloride was added, and the reaction tematufe reacnmg agd mammm'ed at approximately Denture was I uany med fmm 70 F to 125 125 F.,.1 part or cellulose with less than 6 parts over a m m of em t ours t pem v of an esterincation mixture or which at least ture oi 125 F. was maintained ior twelve hours. -i amdnde m wmch 'spbsmnwy The product formed had a tetrachlorethane firstentire "present 18 butyn' wmch stage viscosity (2'1 dilution) of 96 seconds. A gg'imfiff w 51 1 d on the weight 7 .o ose o ,zinc c or e and insubstanmixture or so pounds oi water, 120 pounds oi flafly me ofsulfuflc w,

s. A method of preparing a high viscosity celadded to the completed reaction mixture and the mneflaliwas m at 0 F fir m lulose ester containing at least 30% .propionyl,

which comprises 'esteriiying at a temperature The ester was then precipitated from the to reaching and maintained at 125-160 F with aqueous acid. It had an acetone 65 glinn los twith less, than 6 parts 0: 23m mix are 01 which at least 60 poises and contained 50peroent butyryl. enhydnde, hi h mixtu comin s 1 31?: Example U (based on the weight 01- the cellulose) of line I I I chloride asthe esteriflcation catalyst, is subv20 pounds or cotton linters was mixed'tor one or summc and comm ho M 1". with 20 pounds'of propionic acid eminent when PrP1nY1 W 111 and 10 cc. 0'1 sulfuric acid. :10 pounds oi cotton PrP1n1 content in th m 01 W .llnters was then added and the pretreatment was 3 eontlnued for two hour a mixture or 75 5. A method otpreparing ahigh viscosity collulose ester containing at least 30% of saturated fatty acid groups or 3-4 carbon atoms which comprises esterifying at a temperature reaching and maintained at l25-160 E, 1 part of cellulose, which has been pretreated with acetic acid, with less than 6 parts of an esteriflcation mixture of which at least 60% is anhydride of saturated fatty acid of 3-4 carbon atoms, which mixture contains 15-l00% (based on the weight of the cellulose) of zinc chloride as the esterification catalyst, is substantially free of sulfuric acid and contains a suflicient proportion of saturated fatty acid groups of 3-4 carbon atoms so as to result in a content of those groups in the product of at least 30%.

6. A method of preparing a high viscosity cellulose ester containing at least 30 of saturated fatty acid groups of 3-4 carbon atoms, which comprises esteriiying, at a temperature reaching and maintained at 125-l60 F., 1 part of cellulose with approximately 4.75 parts of an esterification mixture of which at least 60% is anhydride oi saturated fatty acid or 3-4 carbon atoms, which mixture contains 15100% (based on the weight of the cellulose) of zinc chloride as the esteriflcation catalyst, is substantially free of sulfuric acid and contains a suflicient proportion of saturated fatty acid groups of 3-4 carbon atoms so as to result in a content of those groups in the product of at least 7. A method oi preparing a high viscosity ce lulose ester containing at least 30% butyryl, which comprises esterifying at a temperature reaching and maintained at 125-160" F., 1 part of cellulose with approximately 4.75 parts of an esteriilcation mixture of which at least 60% is butyric anhydride, which mixture contains 15-100% (based on the esteriilcation catalyst, is substantially free of sulfuric acid and contains a sumcient portion of butyryl so as to result in 'a butyryl content in the product of at least 30%.

8. A method of preparing a high viscosity cellulose estercontaining at least 30% of saturated fatty acid groups of 3-4 carbon atoms which comprises esterifying at a temperature reaching and maintained at l25-160 F., 1 part of cellulose, which has been pretreated with acetic acid, with approximately 4.75 parts of an esteriiication mixture of which at least is anhydride of saturated fatty acid of 3-4 carbon atoms, which mixture contains 15-10096 (based on the weight of the cellulose) of zinc chloride as the esteriiication-catalyst, is substantially free of sulfuric acid and contains a suilicient proportion of saturated fatty acid groups of 3-4 carbon atoms so as to result in a content of those groups in the product of at least 30%. e

9. A method of preparing a high viscosity cellulose ester containing atleast 30% of saturated fatty acid groups of 3-4 carbon atoms.- which comprises esterifyins, at a temperature reaching and maintained at approximately 125 F., 1 part of cellulose with less than 6 parts of an esteriilcation mixture of which at least 60% is anhydride of saturated fatty acid of 3-4 carbonatoms, which mixture contains Iii-% v(based on the weight of the cellulose) of zinc chloride as the esteriilcation catalyst, is substantially free of sulfuric acid and contains a sumcient proportion of saturated fatty acid groups of 3-4 carbon atoms those groups in so as to result in a content of the product of at least 30%. v

CARL J.MAI.M. LORJNG W. BLANCHARD, Jn. 

